Electric motor, in particular for hand power tools

ABSTRACT

An electric motor for hand power tools has a rotor shaft, a rotor provided with a metal plate pack which is rotatably supported and non rotatably connected with the rotor shaft, the metal plate pack having a plurality of grooves which are spaced from one another in a peripheral direction and provided with a coating of insulating material, a rotor winding received in the grooves provided with the groove coating, the metal plate pack having an end plate composed of insulating material and arranged at each end side of the metal plate pack, the groove coatings and the end plates together with the rotor shaft as shaft ends axially projecting from the end plates being formed as synthetic plastic parts produced by an injection molding.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an electric motor, in particularfor hand powered tools.

[0002] In a known electric motor of this type, a central shaft openingis punched in a metal plate pack of the rotor or the stator, and themetal plate pack with the end plates of insulating material is fitted onthe rotor shaft so that, at both sides of the plate pack the rotor shaftextends axially outwardly with a corresponding shaft portion. Bearingseats for receiving a rotary bearing are formed on the shaft portions,and a pinion for the torque transmission is fixed on one shaft portion.The connection between metal plate pack and the rotor shaft is producedby a plastic injection molding process. Simultaneously a plasticlongitudinal insulation between the rotor shaft and the metal plate packis produced. In the event of failure, it must prevent a voltagepropagation from the rotor winding to the outwardly located, contactingcomponents. The synthetic plastic longitudinal insulation must have acertain thickness because of the corresponding regulations and safetyreasons, and must maintain the required testing voltage. For avoiding avoltage propagation by strong dirtying in the bearing region, and alsoin the event of failure of a commutator, through the armature shaft andthe bearing outwardly, a labyrinth disk is applied on the longitudinalinsulation for creep resistance and distance increase. The grooves inthe plate pack for receiving the rotor winding are coated with pressboard and are closed and impregnated after the winding with the pressedboard.

SUMMARY OF THE INVENTION

[0003] Accordingly, it is an object of the present invention to providean electric motor, in particular for hand powered tools which avoids thedisadvantages of the prior art.

[0004] In keeping with these objects and with others which will becomeapparent hereinafter, one feature of present invention resides, brieflystated, in an electric motor in which the groove coatings and the endplates as well as the rotor shaft with the shaft are injection molded inan injection molding process from synthetic plastic.

[0005] When the electric motor is designed in accordance with thepresent invention, it has the advantage that on the one hand theproduction of the motor is substantially simplified, and on the otherhand, a voltage propagation outwardly in the event of failure isreliably prevented without additional measures. Since the shaft openingis absent and the longitudinal insulation is absent, the magnetic fluxin the iron cross-section is hindered substantially less and theremagnetization losses which are produced in a conventional electricalmachines by high backload and frequency in back iron are substantiallyreduced. The idling speed of the rotor is lowered and thereby thewinding design in the loading point can be improved. With the newcross-sectional design of the metal plates, the field diameter of therotor with the same power can be reduced. By complete synthetic plasticcoating of the metal plate pack, the danger of a wire damage duringwinding process of the rotor winding is lowered. Since the rotor mustwithstand high temperatures during overloads, a high temperatureresistant synthetic plastic or a duroplastic can be utilized.

[0006] In accordance with a preferable embodiment of the invention, aplurality of longitudinal throughgoing axial openings can be provided inthe plates, for filling the synthetic plastic during the injectionmolding process. Preferably, the openings are arranged on web feetbetween the grooves and alternate with the depression for the punchacting, so that in the peripheral region of the metal plate pack, eachdepressions follows an opening and vice versa.

[0007] In accordance with a preferable embodiment of the presentinvention, the rotor winding which is inserted in the grooves of themetal plate pack surrounds its winding heads which project over the endside of the metal plate pack, the end plates and the shaft end and iscoated in a dipping or impregnating process. With this structuraldesign, a very high stability of the rotor is obtained which is requiredfor high rotary speeds. The winding heads additionally contribute to thestabilitation of the armature plate pack and the dipping or impregnationof the rotor winding makes possible glueing and backing of the windingheads, and plates end shaft ends, which together advantageouslyinfluences the strength of the rotor.

[0008] In accordance with a preferable embodiment of the invention, abearing pin for example of steel is injection molded in at least oneshaft end, as an insert aligned with the shaft end. A rotary bearing, inparticular a ball bearing and/or a collector is non rotatably receivedon the pin part which freely projects from the shaft end. The rotarybearing and the collector are preferably pressed on the bearing pin. Adanger of the breakthrough of the voltage to the bearing pin and therebya voltage propagation to the outwardly located components which areaccessible for contacting by a user, does not take place in this case.

[0009] In accordance with a preferable embodiment of the presentinvention, at least one bearing pin extends up to the metal plate packand is firmly connected at an end side with an anchoring disk which isenclosed in the end plate. Forweight reduction, hollow bearing pins andanchoring disks can be formed as one piece deep drawn parts. Theanchoring disk is provided on its disk periphery with a circumferentialset of teeth, in order to improve adherence in synthetic plastic andthereby to provide greater safety against relative movement of thebearing pin and the metal plates.

[0010] In accordance with a preferable embodiment of the presentinvention a pin part of the bearing pin which projects in the endportion outwardly beyond the shaft end has an outer or inner thread forouter or inner screwing of a drive pinion or a drive gear. Alternativelya pinion end is injection molded in the shaft end as an insert which isin alignment with the shaft end. The pinion end with its pinion teethfreely projects outwardly from the shaft end. Bearing pins or pinionends are inserted during the injection molding process in the mold andinjected from synthetic plastic of the shaft end.

[0011] In accordance with a preferable embodiment of the invention, thegrooves which are formed in the synthetic plastic layer are providedwith a groove closure. The groove closures are injection molded in theinjection molding process as a film hinge on the groove coating. Duringthe injection molding process the region of the groove lock serves insynthetic plastic filling process for producing the groove coating. Thegroove locks produced at the end of the filling process are folded afterinsertion of the rotor winding over the groove openings. Tooth stripswhich are formed in an opposite groove flank and produced also duringthe injection molding process, are arrested in a zipper-like manner andsecure the rotor winding in the grooves.

[0012] The novel features which are considered as characteristic for thepresent invention are set forth in particular in the appended claims.The invention itself, however, both as to its construction and itsmethod of operation, together with additional objects and advantagesthereof, will be best understood from the following description ofspecific embodiments when read in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a schematic side view of a rotor for an electric motorin accordance with the present invention;

[0014]FIG. 2 is a perspective view of a metal plate pack of the rotor ofFIG. 1;

[0015]FIG. 3 is a plan view of a metal plate of the metal plate pack ofFIG. 2;

[0016]FIG. 4 is a view showing the section of the metal plate of FIG. 3on an enlarged scale;

[0017]FIG. 5 is a substantially schematic longitudinal section of arotor for a commutator motor in accordance with a further embodiment ofthe present invention;

[0018]FIG. 6 is a view of a bearing pin with an anchoring disk of therotor as seen in direction of the arrow VI in FIG. 5;

[0019]FIG. 7 is a view showing a section of a metal plate of the rotorof FIG. 5, on an enlarged scale; and

[0020]FIG. 8 is a partial longitudinal section of a bearing pin with ananchoring disk and a drive pinion screwed at its end side.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021]FIG. 1 on a side view shows a rotor of an electric motor whichconventionally is composed of a stator and a rotor and used preferablyfor hand power tools. The rotor has a metal plate pack 11 provided withgrooves 12 which are shown in FIG. 2 and spaced from one another by anequal peripheral angle. The metal plate pack 11 is closed at each endside with an end plate 13 composed of insulating material. The metalplate pack 11 which is shown in a perspective in FIG. 2 is assembled ofa plurality of metal plates 14. They are produced in a punching cut andconnected by punch packeting with one another to form the metal platepack 11. One metal plate 14 is shown in FIG. 3. For punch packeting,each metal plate 14 has four depressions 15 which are offset relative toone another by peripheral angle of 90°. They are located directly undera web 23 which remains between the grooves 12.

[0022] The rotor winding of varnish-insulated wire is introduced in anot shown manner into the grooves 12 during a winding process. Forimproving the insulation of the rotor winding from the metal plate pack11, the grooves 12 are provided with a groove coating 16 of insulatingmaterial as shown on an enlarged scale in FIG. 4. The plate metal pack17 is non rotatably connected with a rotor shaft 17, which is rotatablysupported in a stator of the electrical machine in the known manner.

[0023] In the rotor shown in FIG. 1, the groove coating 16 and thegrooves 12, the both end plates 13 and the rotor shaft 17 as the shaftends 171 and 172 axially projecting from the end plates 13 are injectionmolded of synthetic plastic in a joint injection molding process. Abearing pin 18 or 19 is injection molded from steel for each shaft end171, 172 as an insert which is in alignment with the shaft end 171 or172. For this purpose both bearing pins 18, 19 during the injectionmolding process are inserted in the injection mold and enclosed bysynthetic plastic of the shaft end 171, 172. A bearing seat for a rotarybearing is formed on each pin part 181 or 191 of the bearing pin 18 or19, which freely projects outwardly beyond the shaft end 171 or 172.

[0024] A thread 20 for screwing of a driven pinion for torquetransmission is cut in the end portion of the pin part 181. In the caseof the electrical machine formed as a commutator motor, a commutator isfitted on the shaft end 172 and in a known manner is connected to therotor windings. As can be seen from FIG. 4, the grooves in the metalplate pack 11 are closed after insertion of the rotor winding, by agroove closure 21. The groove closure 21 is injection molded during theinjection molding process of the groove coating 16, the end plates 13,and the shaft ends 171, 172, as a film hinge on the groove coating 16 ineach groove 12. After insertion of the rotor winding, the grooveclosures 21 are folded by 90°and arrested at the opposite groove side inan available toothed strip 22 which is also injection molded, in form ofa friction lock.

[0025] In an alternative embodiment of the invention, instead of theinjection molding of the bearing pin 18 in the shaft end 171, a pinionend is injection molded as an insert which is in alignment with theshaft end 171. This pinion end projects with its pinion teeth outwardlybeyond the shaft end 171 and makes unnecessary the thread 20 on thebearing pin 18 and subsequent screwing of a pinion on the thread 20 ascan be seen from TD FIG. 1. As the bearing pin 181, also the pinion endcan be introduced during the injection molding process into theinjection mold and thereby injection molded from the synthetic plasticof the shaft end 171.

[0026] In a further alternative embodiment of the invention, the bearingpin 191 which is injection molded in the shaft end 172 is not formed asa steel insert. Instead, the bearing pin is injection molded of onepiece with the shaft end 172. This is possible when the bearing pin isfitted over a ball bearing in the stator and the inner ring of the ballbearing is non rotatably arranged on the injection molded bearing pin.

[0027] FIGS. 5-8 show a further embodiment of a rotor for an electricmotor, here a commutator motor. Here also the groove coatings areinjection molded in the grooves 12 of the plate pack 11, end plates 13and the shaft ends 171, 172 which form the rotor shaft 17, in aninjection molding process and from synthetic plastic. The metal platepack 11 is also assembled from the metal plates 14 by punch packeting,and for this purpose depressed depressions 15 are provided on each metalplate 14 and offset relative to one another by the same peripheralangle. As shown in FIG. 7, the depressions 15 are arranged directlyunder a web 23 which remains between the grooves 12, and the depressions15 are associated with each second web 23. For improving the stabilityof the metal plate pack 11, all metal plates 14 are provided withopenings 24 which are offset relative to one another by the sameperipheral angle. They are also located directly under a web 23 whichremains between the grooves 12. Since the openings 24 are associatedwith each second web 23, one depression 15 always alternates with oneopening 24 in the peripheral direction of the metal plates 14 as can beseen from FIG. 7.

[0028] After punch packeting longitudinal openings which are assembledfrom the openings 24 and arranged in alignment with one anothercompletely extend through the metal plate pack 11. During the injectionmolding process of the end plates 13, the shaft ends 171, 172 and thenot shown groove coatings these longitudinal openings are completelyfilled with synthetic plastic due to flow properties of the syntheticplastic. The rotor winding 25 which similarly to the embodiment of FIGS.1-4 is inserted in the grooves 12 provided with the groove coatings andgroove locks, surrounds the end plates 13 and the shaft ends 171, 172with the winding heads 251 which extend outwardly beyond the end sidesof the metal plate pack 14 or in other words the end plates 13.

[0029] The rotor winding 25 is coated in a dipping or impregnatingprocess. Thereby the winding heads 251 are additionally baked with theend plates 13 and the shaft ends 171, 172, so that as a whole thestrength of the rotor is further increased.

[0030] The bearing pins 18, 19 are also injection molded in the shaftends 171, 172. However, the bearing pins 171, 172 extend up to the metalplate pack 11 and are firmly connected at one end side with theanchoring disk 26 which is locked in the corresponding end plate 13. Theanchoring disk 26 which is shown in a plan view in FIG. 6 is provided onits periphery with a set of teeth 27 for an improved adherence with thesynthetic plastic of the end plate 17. This reliably prevents a turningof the bearing pin 18 or 19 in the shaft end 171 or 172 under the actionof high torques applied to the bearing pins 18,19. The bearing pins18,19 which are formed here hollow, together with the anchoring disk 26are produced as deep drawn parts and injection molded during injectionmolding process as inserts. In the embodiment of FIG. 5 an impeller 20of a fan which serves for cooling of the electric motor is arranged onthe shaft end 171. A commutator 29 and a ball bearing 30 for supportingthe rotor in the stator are pressed on the bearing pin 19 which projectsoutwardly beyond the shaft end 172.

[0031] As can be seen from FIG. 8, an inner thread 34 is formed in thehollow bearing pin 18, and a drive pinion 31 with an axial end 311 isscrewed in it. Alternatively, as shown in FIG. 9, a drive pin 31provided with a center opening can be fitted on the bearing pin 18. Forthis purpose the pin end is stepped, for forming an abutment shoulder 32of a different diameter. The drive pinion 31 which abuts against theabutment shoulder 32 is clamped against the abutment shoulder 32 by aclamping screw 33 screwed into the inner thread 34 in the bearing pin18.

[0032] It will be understood that each of the elements described above,or two or more together, may also find a useful application in othertypes of constructions differing from the types described above.

[0033] While the invention has been illustrated and described asembodied in electric motor, in particular for hand power tools, it isnot intended to be limited to the details shown, since variousmodifications and structural changes may be made without departing inany way from the spirit of the present invention.

[0034] Without further analysis, the foregoing will so fully reveal thegist of the present invention that others can, by applying currentknowledge, readily adapt it for various applications without omittingfeatures that, from the standpoint of prior art, fairly constituteessential characteristics of the generic or specific aspects of thisinvention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.
 1. An electric motor for hand powertools, comprising a rotor shaft; a rotor provided with a metal platepack which is rotatably supported and non rotatably connected with saidrotor shaft, said metal plate pack having a plurality of grooves whichare spaced from one another in a peripheral direction and provided witha coating of insulating material; a rotor winding received in saidgrooves provided with said groove coating, said metal plate pack havingan end plate composed of insulating material and arranged at each endside of said metal plate pack, said groove coatings and said end platestogether with said rotor shaft as shaft ends axially projecting fromsaid end plates being formed as synthetic plastic parts produced by aninjection molding.
 2. An electric motor as defined in claim 1 , whereinsaid metal plate pack is provided with a plurality of longitudinallyextending axial openings which are filled with synthetic plastic duringinjection molding.
 3. An electric motor as defined in claim 1 , whereinsaid rotor winding which is inserted in said grooves of said metal platepack has winding heads which project outwardly beyond end sides of saidmetal plate pack and surround said end plates and said shaft ends, saidwinding heads being coated by a dipping or impregnating process.
 4. Anelectric motor as defined in claim 1 ; and further comprising a bearingpin which is injection molded in at least one of said shaft ends as aninsert in alignment with said shaft end; and a pin part which freelyprojects from said shaft end and formed for receiving an additionalelement.
 5. An electric motor as defined in claim 4 , wherein saidbearing pin is composed of steel.
 6. An electric motor as defined inclaim 4 , wherein said pin part is formed for non-rotatably supporting aball bearing.
 7. An electric motor as defined in claim 4 , wherein saidpin part is formed for non rotatably supporting a commutator.
 8. Anelectric motor as defined in claim 4 , wherein said bearing pin ishollow.
 9. An electric motor as defined in claim 4 , wherein saidbearing pin extends up to said plate metal pack; and further comprisingan anchoring disk which is enclosed in said end plate and is fixedlyconnected with said bearing pin at an end side of the latter.
 10. Anelectric motor as defined in claim 9 , wherein said anchoring disk isprovided with a set of teeth on a periphery of said disk.
 11. Anelectric motor as defined in claim 4 , wherein said pin part whichextends outwardly beyond said shaft end has an end portion provided witha thread; and further comprising a drive pinion which is screwed withsaid thread.
 12. An electric motor as defined in claim 11 , wherein saidthread is formed as a thread selected from the group consisting of anouter thread and an inner thread for correspondingly outwardly andinwardly screwing said drive pinion.
 13. An electric motor as defined inclaim 1 , wherein said bearing pin has an abutment shoulder, said drivepinion being arranged on said bearing pin and clamped against saidabutment shoulder of said bearing pin by a clamping screw which isscrewed into an inner thread of said bearing pin which is at leastpartially hollow.
 14. An electric motor as defined in claim 1 , whereinsaid grooves in said metal plate pack are provided with a groove lockwhich during injection molding is molded of synthetic plastic on saidgroove coatings as a film hinge.
 15. An electric motor as defined inclaim 1 ; and further comprising a bearing pin which is injection moldedof one piece on at least one of said shaft ends, for receiving a ballbearing.